Cannabis shows inconsistent benefits for pain, PTSD

Chronic pain and posttraumatic stress disorder are among the top reasons given by patients seeking medical marijuana in states where it is legal, but there is little scientific evidence to support its  value for treating either condition, based on the results of a pair of systemic evidence reviews conducted by the US Department of Veterans Affair. 

Data on the use of cannabis and related products to treat PTSD and chronic pain are too limited to assess effectiveness, the researchers noted.

In the PTSD study, researchers found no significant evidence to support the effectiveness of cannabis for relieving symptoms. The researchers assessed data from two systematic reviews and three primary studies. 

One of the larger studies (included in one of the systematic reviews) included 47,000 veterans in intensive treatment programs designed to ease their PTSD symptoms, run by VA 1992-2011.  In fact, after controlling for demographic factors and other compounding variables, individual who either continued or initiated cannabis use showed worse PTSD symptoms than did non-users after four months.

Findings from (randomized, controlled trials) are needed to help determine whether and to what extent cannabis may improve PTSD symptoms, and further studies also are needed to clarify harms in patients with PTSD, the researchers noted.

In the review of chronic pain literature, researchers examined 27 trials, 11 reviews, 32 primary studies.

Across nine studies, intervention patients were more likely to report at least 30 percent improvement in pain, the investigators said. But this finding was specific to tetrahydrocabinol (THC), the researchers said, and evidence of the  ability of cannabis to relieve other type of pain, such as cancer pain and multiple sclerosis, was insufficient.

The researchers found only weak evidence that cannabis use was associated with development of psychotic symptoms and moderately strong evidence that cannabis use was associated  with impaired  cognitive function in the general population. However, the confidence in the findings is limited by inconsistent findings among included studies, inadequate assessment of exposure, and inadequate adjustment for confounding among the studies.

Although no significant differences were noted in rates of adverse events between cannabis users and nonusers, some data suggested users had  an increased risk for short-term adverse events that ranged from dizziness to paranoia and attempted suicide. Other potential harms associated with cannabis use included decreased lung function, increased risk of complications from infectious diseases, cannabis hyperemesis syndrome, and increase risk of  violent behavior.